1,5-AG is a compound which is present in the cerebrospinal fluid and plasma of humans and it is reported that its quantity is reduced in plasma with certain diseases, particularly with diabetes. It has not been known the presence of an enzyme that oxidizes this 1,5-AG. The assay for 1,5-AG has been hitherto performed mainly based on gas chromatography (J. Biochem., 90, 157-162 (1981)).
However, the prior art method requires techniques for pretreatment of specimen and maintenance and control of analysis equipment to high degree and a simple method of assay for 1,5-AG has been demanded.